In recent years, EMC has gained an ever increasing impact on the success of products in the automotive area. Despite constantly rising requirements with regard to the performance of such products normally entailing an increased electromagnetic activity, their EMC characteristics have to improve as well. For this purpose, new methods and systems for improving EMC characteristics are required.
A conventional and accepted method for improving EMC characteristics is based on frequency modulation of the clock signal within electronic circuits. However, this method bears the disadvantage that —due to the frequency modulation—the error of the clock signal (jitter) is increased.
Specifically, for a frequency modulation of the clock signal that significantly contributes to improved EMC characteristics, the jitter increases by an amount which may cause that common communication interfaces do no longer operate correctly.
For instance, an acceptable jitter of a clock signal for a system comprising an exemplary communication interface may lie in the order of 10 to 15 ns. To this jitter budget a corresponding conventional clock source which is not frequency modulated may already contribute a jitter of 1 to 5 ns.
However, a frequency modulation of said clock source with a relatively low modulation frequency fMOD=100 kHz compared to the frequency of the clock signal fCLK=400 MHz and a modulation amplitude MA=2% causes a mean additional modulation jitter of 50 ns, as an example according to the equation
      Jitters    ⁡          [      ns      ]        =            2500      ×      M      ⁢                          ⁢              A        ⁡                  [          %          ]                                    f        mod            ⁡              [        kHz        ]            for triangular modulation.
Hence, the total jitter of the modulated clock source ranges between 51 ns and 55 ns which clearly exceeds the above-mentioned acceptable jitter budget of 10 to 15 ns. This precludes the modulated clock source from being used for the exemplary communication interface.
As a result, frequency modulation has not been used in many applications such as for example automotive applications at a mass production level.
Instead, different previous solutions have been established that are based on a second independent and precise clock signal to reduce the jitter of a first clock signal. However, these prior art solutions bear several disadvantages. For instance, they require a further phase locked loop (PLL) just for the above-mentioned purpose. This—in turn—is only available at the cost of increased power consumption and an increased demand for area on an integrated circuit.
For these or other reasons, there is a need for the present invention.